nA+-k+-2Cl-cotransporters (NKCC) are important in renal salt reabsorption and secretion by reabsorptive and secretory epithelia. The NKCC also function in maintenance and regulation of cell volume in both epithelial and non-epithelial cells. However, the role of the NKCC in the central nervous system (CNS) have not been defined. The long-term goal of this research is to understand function and regulation of the NKCC in the CNS under physiological as well as pathological conditions such as ischemia. Our pilot studies described in this proposal suggest that the NKCC are essential in maintenance of K+ homeostasis in astrocytes and they also appear to be involved in glutamate (Glu)-mediated neurotoxicity. There are four Specific Aims to test our hpotheses. Aim 1: Characterize high [K+]o-mediated stimulation of the NKCC activity in primary astrocyte cultures. The objectives are: 1). to verify that high [K+]o causes stimulation of the NKCC; 2). to determine whether the high [K+]o mediated stimulation of the NKCC is due to an increase in intracellular [Ca++]. Aim 2: Determine whether high [K+]o- mediated stimulation of the NKCC causes astrocyte swelling and non-vesicular release of Glu. The objectives are to investigate: 1). whether the NKCC contributes to accumulation of intracellular Na+, C1 and cell swelling under [K+]o; 2). whether inhibition of the NKCC activity could significantly increase [3H]-L-Glu uptake, while blocking of high [K+]-evoked release of Glu from astrocytes. Aim 3: Investigate whether stimulation of the NKCC contributes to Glu-mediated neuronal toxicity. The objectives are to investigate: 1). whether the NKCC contributes to Glu- mediated increase in [C1-]i and neuronal swelling; 2). whether inhibition of the NKCC activity could protect cells from Glu- induced damage. Aim 4: Determine whether ischemia-induced cell damage is reduced when the NKCC activity is transiently inhibited by a local administration of bumetanide in brain. This study will be performed in an in vivo cerebral ischemic model.